1. Field of the Invention
The present invention relates to location measurement, and in particular to accurately determining the location of a station in a wireless network.
2. Related Art
The IEEE 802.11 family of standards governs wireless networking transmission. A proposed amendment to these standards, 802.11v, would provide a range of benefits including, but not limited to, advanced energy conservation, timing synchronization, and real time location service (RTLS). The RTLS is meant to allow tracking of compatible Wi-Fi enabled devices to facilitate asset tracking as well as security and emergency services.
In general, knowing the coverage zone (e.g. a radius r) of an access point (AP) and that a Wi-Fi client (hereinafter station) is associated with that AP can provide a rudimentary approximation of the location of that station (i.e. within r distance). To get a more accurate location, multiple APs can be used simultaneously, wherein each AP has a known coverage zone.
In another technique, a received signal strength indicator (RSSI) can be measured based on signals received by each AP from the station. A stronger RSSI means that a station is closer to the AP, whereas a weaker RSSI means that the station is farther from the AP. Multiple RSSI measurements, when compiled by a central processer, can be used to provide a relatively accurate location for the station.
Unfortunately, using either the AP zone technique or the RSSI technique still cannot consistently provide the accuracy needed for asset tracking as well as security and emergency services. Therefore, a need arises for a technique that can consistently provide accurate locating using a wireless network.